Oil and gas well completion and production techniques often include hydraulic fracturing in low permeability rock formations to produce hydrocarbons, such as in shale and chalk rock formations. Hydraulic fracturing, often abbreviated “Frac,” is a technique in which high hydraulic pressures often in excess of 20,000 pounds per square inch on the surface are used for opening channels in rock formations through which hydrocarbons can flow to production wells. During hydraulic fracturing, a fluid is pumped into a reservoir rock under high pressure where it cracks or fractures the rock. Treatment chemicals and solids called proppants are carried in suspension by the fluid pumped into the fractures. When the pressure is released, the fractures close on the proppants leaving open channels through which hydrocarbons can flow.
Specialized pumps are used to deliver fracturing fluids at sufficiently high rates of pressure to complete the hydraulic fracturing procedure, often called a “Frac job.” These pumps are often called Frac pumps and typically have a drive end and a fluid end. The drive ends include motors which provide power. Fluid ends for current modern day Frac pumps bear a resemblance to automotive engine blocks. The fluid ends have pump chambers into which plungers are pushed, powered by the drive ends, to place the frac fluids under high pressures and move the frac fluids through the pump chambers. Current Frac pumps are typically classified as either triplex pumps or quintuplex type pumps. The triplex Frac pumps have three fluid passages extending transversely through a fluid end and three plungers which reciprocate to pressurize and move the Frac fluids through respective flow passages. Quintuplex Frac pumps have five fluid passages extending transversely through a fluid end and five plungers extending into respective ones of the flow passages for pressurizing and moving fluids through the respective flow passages. Triplex and quintuplex Frac pumps will typically have power ends which are powered by engines often rated from 2,000 horsepower to 3,000 horsepower, connected to the power ends by torque converters and transmissions.
The fluid ends of high pressure pumps have valves that control the flow of fluids to and from the plungers. Suction valves pass fluid into a respective flow passage when a respective plunger is moved outward from within a fluid end and seal against fluid flow when the plunger is moved inward into the fluid end. Suction valves are kept closed by springs until retraction of plunger and charge pump pressure cause suction valves to open. Discharge valves are configured to seal respective flow passages and not pass fluid when a plunger is moved outward from within a fluid end, and pass fluid through a discharge port when the plunger is pressed inward into the fluid end. Discharge pressure in the treating line and valve springs on discharge valves keep discharge valves closed until forward motion of the plunger builds pressure, forcing suction valves to close and discharge valves to open. Pressure buildup in fluid end chambers is greater than in treating lines causing the discharge valves to open, forcing fluid into the discharge line.
Power ends transmit torque from engines into reciprocating motion for moving pump plungers to power the fluid ends of conventional frac pumps. One or more pinion gears are mounted to a drive shaft extending from an engine transmission into a housing for the power end. The pinion gears engage ring gears to turn a crank shaft to which bearing housings with mating connecting rods are mounted. The connecting rods move crossheads and extension rods which are connected to pump plungers. The plungers are reciprocated in a pump chamber to move fluid through the fluid end pump.
Fluid ends and power ends have many parts that are releasably fastened to one another so that components may be easily repaired or replaced. Frac pump fluid end and power end components are often replaced at regular scheduled maintenance intervals to prevent failure and costly down time during fracturing operations. Improvements which increase the service life of Frac pump fluid end and power end components are highly desired.
Suction and discharge covers for fluids ends are cylindrically shaped plugs which provide access for replacing fluid end valves and plunger components. Elastomeric seals, such as O′rings, seal between the covers and the walls of ports in which the covered are disposed. Under high pressure these elastomeric seals will often leak.